﻿<Window
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Title="Show TextBox"
  Width="300"
  Height="100">
  
  <Grid ShowGridLines="True">
    <Grid.RowDefinitions>
      <RowDefinition Height="20"/>
      <RowDefinition Height="Auto"/>
      <RowDefinition Height="30"/>
    </Grid.RowDefinitions>
    <TextBox Grid.Row="1" x:Name="txt"/>
  </Grid>
</Window>